1. Field of the Invention
The present invention relates to an image reading apparatus which automatically conveys and read an original sheet and an image forming apparatus having the image reading apparatus.
2. Description of the Related Art
Conventionally, in case of reading an image of one original sheet in a bundle of original sheets where one-sided original sheets and double-sided original sheets are mixedly stacked, there has been used an image reading apparatus capable of reading the side where image exists, by automatically detecting whether the original sheet is the one-sided original sheet or the double-sided original sheet.
As an example, Japanese Patent Application Laid-Open No. 2005-244756 discloses an image reading apparatus where an image existence/non-existence detecting sensor detects existence or non-existence of image on an image side of an conveying original sheet so that an image reading unit can read the image from only the image existing side without reading an image from the image non-existing side of the original sheet.
As another example, Japanese Patent Application Laid-Open No. 2005-078464 discloses an image reading apparatus where a bundle of original sheets is illuminated with an electromagnetic wave so as to detect stacked positions of the original sheets accordingly a delay time of a reflected or transmitted electromagnetic wave, and information on a surface of or in an inner portion of the bundle of original sheets is detected according to a time-varying waveform of the reflected or transmitted electromagnetic wave, so that the image reading can be performed in the bundle state.
However, in a technique of Japanese Patent Application Laid-Open No. 2005-244756, since existence or non-existence of image of the original sheet cannot be detected if the original sheet is not fed, the original sheets are fed sequentially to detect the image. Therefore, the reading of image for detecting the existence or non-existence of image and the reading of image for the original sheet need to be sequentially performed, so that the reading time is increased. In addition, since a to-be-transferred sheet cannot be fed if the detecting of the existence or non-existence of image is not performed, the productivity of image forming is decreased.
In addition, in a technique of Japanese Patent Application Laid-Open No. 2005-078464, in order to read all the image information in the bundled state, the image reading apparatus becomes complicated and expensive for reading position accuracy or the like. In addition, since the reading time is increased, the productivity of image forming is decreased.
The present invention provides an image reading portion capable of decreasing an image reading time and of reading image information with a high accuracy at low costs and an image forming apparatus having the same image reading portion.